[IMP-dev] Particle refines

This patch adds particle refines to IMP. There is a base class in <IMP/ ParticleRefiner.h> and a couple in <IMP/particle_refiners>. The current particle refines cover an bond with a set of spheres (created on the fly) and move down one level in the hierarchy. I added some new meothods and classes to the python test base class too.

SWIG was having problems with figuring out that Particle Refiner was not a virtual class when I had all the methods be virtual, so they are now all non-virtual.